This invention relates to a thermally stable diamond abrasive compact body.
Diamond abrasive compacts are well known in the art and consist essentially of a mass of diamond abrasive particles present in an amount of at least 70 percent, preferably 80 to 90 percent, by volume of the compact bonded into a hard conglomerate. Compacts are polycrystalline masses and can replace single large crystals in many applications. Diamond abrasive compacts are also known as polycrystalline diamond or PCD.
Diamond compacts will typically contain a second phase uniformly distributed through the diamond mass. The second phase may contain a dominant amount of a catalyst/solvent for diamond synthesis such as cobalt, nickel or iron. Diamond compacts having second phases of this nature will generally not have thermal stability above 700.degree. C.
Diamond abrasive compacts may be used alone or as composite compacts in which event they are backed with a cemented carbide substrate. Composite diamond abrasive compacts wherein the second phase contains a diamond catalyst/solvent are widely used in industry.
Examples of composite diamond abrasive compacts are described in U.S. Pat. No. 3,745,623 and British Patent Specification No. 1,489,130.
Diamond abrasive compacts of the type described above are thermally sensitive above a temperature of about 700.degree. C. There are, however, described in the literature and in commercial use several diamond abrasive compacts which are thermally stable above 700.degree. C. For example, U.S. Pat. No. 4,224,380 describes a thermally stable diamond compact which comprises self-bonded diamond particles comprising between about 70% and 95% by volume of the product, a metallic phase infiltrated substantially uniformly throughout the product, the phase comprising between about 0,05% and 3% by volume of the product and a network of interconnected, empty pores dispersed throughout the product and defined by the particles and the metallic phase, the pores comprising between 5% and 30% by volume of the product.
U.S. Pat. No. 4,534,773 describes a thermally stable diamond abrasive compact which comprises a mass of diamond particles present in an amount of 80 to 90% by volume of the body and a second phase present in an amount of 10 to 20% by volume of the body, the mass of diamond particles containing diamond-to-diamond bonding to form a coherent, skeletal mass and the second phase containing nickel and silicon, the nickel being in the form of nickel and/or nickel silicide and the silicon being in the form of silicon, silicon carbide and/or nickel silicide.
British Patent Publication No. 2158086 describes a thermally stable diamond abrasive compact similar to that described in U.S. Pat. No. 4,534,773 save that the second phase consists essentially of silicon in the form of silicon carbide and/or silicon.
EPA 0261948 published Mar. 30, 1988 describes a method of making a composite diamond abrasive compact comprising a thermally stable diamond compact bonded to a cemented carbide substrate including the steps of forming an unbonded assembly comprising a thermally stable diamond compact comprising a mass of diamond particles containing diamond-to-diamond bonding to form a coherent, skeletal mass, and a second phase uniformly distributed through the diamond mass, a cemented carbide substrate and a layer of nickel or a nickel-rich alloy between the compact and the substrate, placing the unbonded assembly in the reaction zone of a high pressure/high temperature apparatus, subjecting the unbonded assembly to a temperature of at least 1000.degree. C. and simultaneously a pressure of at least 30 kilobars for a time sufficient to cause bonding to occur between the compact and the substrate and removing the composite diamond abrasive compact from the reaction zone.
U.S. Pat. No. 4,380,471 describes a process for simultaneously cementing diamond particles together and affixing the cemented diamond particles to a substrate comprising the steps of:
(a) disposing within a refractory metal container a mass of silicon-containing metal, a quantity of diamond powder, a cemented carbide body and a layer made of a barrier metal selected from the group consisting of tantalum, vanadium, molybdenum, zirconium, tungsten and alloys thereof, the layer of barrier material being disposed between the cemented carbide and at least a portion of the quantity of diamond powder and the quantity of diamond powder being disposed between the silicon atom-containing metal and the cemented caride body to form an assembly, and PA1 (b) simultaneously applying heat and pressure to the assembly to melt the silicon atom-containing metal and cause the molten metal to infiltrate the diamond powder adjacent to and make contact with the layer of barrier material. PA1 (i) preparing an assembly of a metallic layer, a mass of diamond particles on the metallic layer and a layer of the component or components necessary to form the second phase on the diamond particles, this component or these components having a melting point lower than that of the metallic layer; and PA1 (ii) subjecting the assembly to conditions of elevated temperature and pressure for a period sufficient to produce the diamond abrasive compact, the temperature being controlled such that there is minimal infiltration of the metallic layer into the diamond mass.
It is to be noted that this method involves a one stage application of heat and pressure to the assembly.